The FBI “most wanted” mugshot shows a tough, swarthy figure, his hair in a jailbird crew-cut. The $10 million price on his head, meanwhile, suggests that whoever released him from US custody four years ago may now be regretting it.

Taken during his years as a detainee at the US-run Camp Bucca in southern Iraq, this is the only known photograph of Abu Bakr al-Baghdadi, the new leader of al-Qaeda in Iraq and Syria, now known as the Islamic State of Iraq and al-Shams (ISIS). But while he may lack the photogenic qualities of his hero, Osama bin Laden, he is fast becoming the new poster-boy for the global jihadist movement.

Well-organised and utterly ruthless, the ex-preacher is the driving force behind al-Qaeda’s resurgence throughout Syria and Iraq, putting it at the forefront of the war to topple President Bashar al-Assad and starting a fresh campaign of mayhem against the Western-backed government in Baghdad.

This week, his forces have achieved their biggest coup in Iraq to date,seizing control of government buildings in Mosul, the country’s third biggest city, and marching further south to come within striking distance of the capital, Baghdad. Coming on top of similar operations in January that planted the black jihadi flag in the towns of Fallujah and Ramadi, it gives al-Qaeda control of large swathes of the north and west of the country, and poses the biggest security crisis since the US pull-out two years ago.